from abc import ABCMeta,abstractmethod


class Animal(metaclass=ABCMeta):

    @abstractmethod
    def say(self):
        raise NotImplementedError


class Cat(Animal):

    def say(self):
        print('喵喵喵')


class Dog(Animal):

    def say(self):
        print('汪汪汪')


animal = Cat()
animal.say()